The invention relates to dental handpiece of the type comprising a hollow body, a central rotary shaft rotatably mounted in the body, a tool-gripping chuck carried by a forward end of the shaft, a first chuck-actuating sleeve slidably axially mounted on the shaft between a first position corresponding to a tool-gripping position of the chuck and a second position corresponding to a tool-release position of the chuck, a spring biasing the gripping sleeve axially relative to the shaft, at least one radially-movable ball cooperating with a generally conical wall of the first sleeve, and an external second chuck-actuating sleeve on the body cooperating with the ball to radially inwardly move the ball to axially move the first sleeve against the action of the biasing spring.
In known handpieces of this type, the chuck is held in a tool-gripping position by pressing the balls inwardly against the generally conical wall of the first sleeve, and holding the balls in this position by an inner fixing cone. When the central shaft rotates, the first sleeve also rotates together with the balls and the fixing cone, so that it is necessary to carefully balance the parts. Also, the fixing cone is coupled with the external second actuating sleeve by an arrangement designed to reduce friction between these two parts. For example, the second sleeve is connected to the fixing cone by a sliding piece and two guide pieces, the sliding piece being lodged in a groove in the fixing cone. However, there is still a risk of friction being set up between the sliding piece and the fixing cone when the latter is rotated.
An aim of the invention is to avoid the aforementioned disadvantages, and particularly to eliminate any friction between the parts of the chuck actuating device when the handpiece shaft is rotated.